LA2A Noisiest resistors

[Roland808]

Hi all - I’m upgrading a Lin2A, which is fantastically grabby but which has an insanely high noise floor. Not making this up—it’s unusually high even for a clone.

Assuming the trad LA2A schematic which I won’t bother reposting here because it’s all over Ask Jeeves, which resistors contribute most to the noise floor? All of the 220ks seem likely culprits, but I’ll defer to your expertise.

Also will an upgrade to Black Lion tubes yield juice worth the expensive squeeze?

Just trying to get this thing to usable. Thanks!

 

[emrr]

Cathode and plate in the first stage. It's always whatever's first and at lowest gain.

 

[Clbraddock]

I’d think R6 and R7 (right after the input transformer) would be culprits to, yes? Any noise they introduce is getting amplified by the amplification stage.

 

[meloamantis]

Focus on replacing the 220k resistors by using metal film resistors instead of carbon film or carbon composition ones, as metal film types have lower noise levels and better tolerance

 

[emrr]

I’d think R6 and R7 (right after the input transformer) would be culprits to, yes? Any noise they introduce is getting amplified by the amplification stage.

Turn gain all the way down - is there noise? Then it's after the gain control. Short V1A grid? Better? Swap the two 12AX7. B better? Etc.

 

[ZHOUJUN]

Noise will only occur when the resistor fails or has a large offset. I tried carbon core, carbon film, and metal resistors. No matter what they are, healthy resistors will not produce obvious noise, but will only subtly change the color of the sound. Noise may be caused by the aging of the transformer, electrolytic cap, electronic tube or unreasonable wiring.